Can one person hold both principal designer roles?

The certification route

A client is treated as complying with the requirement in paragraph (1) if, instead of appointing a person for the purposes of these Regulations, they certify, in writing, that the person who is the CDM principal designer, or, as the case may be, the CDM principal contractor, is treated as appointed as the principal designer or, as the case may be, the principal contractor, for the purposes of these Regulations.

Three points follow from the wording.

• It is the client's certificate. Regulation 11D(2) does not say the CDM principal designer has to countersign it or agree to it.
• It is a full appointment. Regulation 11Q(2) says references in Part 2A to an appointment under 11D include one certified under 11D(2). The certified firm carries every Building Regulations principal designer duty in regulation 11M, including the document explaining its arrangements within 28 days of the appointment ending (11M(5)(b)).
• Competence is not certified with it. A person must not act as principal designer unless it meets the competence requirements in regulations 11F and 11G (11E(7)(a)). Those tests are about designing work that complies with the Building Regulations, not about health and safety coordination.

Three ways one firm ends up with both roles

1. Two express appointments. The client appoints the same firm to each role, in writing, under each set of regulations. This is the clear way to do it.
2. Certification under 11D(2). The client appoints a CDM principal designer and certifies that it is treated as the Building Regulations principal designer too.
3. By default on a home project. If a domestic client appoints nobody, the designer in control of the design phase becomes the Building Regulations principal designer (11C(2)(a)), and the designer in control of the pre-construction phase becomes the CDM principal designer (CDM regulation 7(2)(a)). Where one designer controls both, it holds both roles without anyone deciding it.

Where it goes wrong

The accidental version: a client appoints a specialist CDM consultant and signs an 11D(2) certificate as a formality. On paper the Building Regulations appointment exists. In practice nobody is coordinating the design for Building Regulations compliance.

The gap shows at the end. The completion notice to the council must include a statement, signed by each principal designer, confirming it fulfilled its Part 2A duties (regulation 16(4A)(e)). With a registered approver the same statement goes to the approver (Building (Registered Building Control Approvers etc.) (England) Regulations 2024, regulation 18). A firm that never took on the role cannot honestly sign it, and the notice then has to give the reasons instead (16(4B)).

ClearCDM sets out its own position, and why the certification route should not be used to name it, in can the same person be both principal designers?.

Setting it up properly

1. Decide who controls the design. Part 2A needs a designer with control over the design work (11D(1)). That is normally whoever leads the design. The Building Safety Regulator's guidance says the principal designer should be "part of the design team".
2. Ask each firm which roles it provides. Get the answer in its appointment or fee letter, role by role.
3. Use 11D(2) only where the CDM principal designer confirms it will act as the Building Regulations principal designer too. Otherwise make a separate written appointment.
4. Tell building control. Name the principal designer on a full plans application where known (regulation 14(1)(c)). An appointment made after the application or building notice must be notified within 14 days; on a domestic project the appointee gives that notice (11O(5) and (7)).

What this means for you

One firm holding both roles is lawful. Make it a decision, not an accident: two appointments in writing, or a certificate under 11D(2) that the firm has agreed to. For how the roles differ, see Building Regulations and CDM principal designers compared; for the Building Regulations role itself, see the Building Regulations principal designer.

This guide covers England; Wales has its own dutyholder provisions for Building Regulations. Parallel Architecture coordinates Building Regulations information as part of its design work. Get in touch to talk a project through.